Best languages/software for GUI design

Hi all. Say if someone approached you and said ĎI have designed a handheld game console that has a digital screen thatís going to be manufactured, but it needs the GUI designedí. How would you design the GUI (in what languages & using what programs) so that it could be implemented on the product?

Depends on the expectations. If you want to create a GOOD QUALITY GUI, with the oily-greasy-super-responsive feeling of a native interface, then it's a compiled language, running natively on the CPU. That's basically C++ these days.